Heat-sensitive stencil sheet

ABSTRACT

A HEAT-SENSITIVE STENCIL SHEET COMPRISING: (A) A TIN POROUS SUPPORT HAVING A THERMOPLASTIC RESIN FILM BONDED TO ONE SURFACE THEREOF WITH AN ADHESIVE CONTAINING AT HEAT-SENSITIVE COMPONENT WHICH UNDERGOES A VISIBLE COLOR CHANGE AT A TEMPERATURE OF FROM ABOUT 80* C. TO 180*C. TOGETHER WITH AT LEAST ONE HEAT-FUSIBLE COMPOUND WHICH IS A METALLIC SALT OF A FATTY ACID CONTAINING FROM ABOUT 10 TO 22 CARBON ATOMS AND FORMS A TRANSPARENT MELT AT A TEMPERATURE OF FROM ABOUT 50*C. TO 150*C.; OR (B) A THIN POROUS SUPPORT HAVING A THERMOPLASTIC FILM BONDED TO ONE SURFACE THERE WITH AN ADHESIVE, SAID FILM BEING COATED WITH A MIXTURE CONTAINING A HEAT-SENSITIVE COMPONENT WHICH UNDERGOES A VISIBLE COLOR CHANGE AT A TEMPERATURE OF FROM ABOUT 80*C. TO 180*C. TOGETHER WITH AT LEAST ONE HEAT-FUSIBLE COMPOUND WHICH IS A METALLIC SALT OF A FATTY ACID CONTAINING FROM ABOUT 10 TO 22 CARBON ATOMS AND FORMS A TRANSPARENT METAL AT A TEMPERATURE OF FROM ABOUT 50*C. TO 150*C.

United States Patent O 3,715,263 HEAT-SENSITIVE STENCIL SHEET Keislli Kubo, Yokohama, Kiyoshi Sakai, Tokyo, Takashi Sato, Urawa, and Itaru Nalramura, Yokohama, Japan, assignors to Ricoh Co., Ltd., Tokyo, Japan No Drawing. Filed Nov. 13, 1970, Ser. No. 89,453 Claims priority, application Japan, Nov. 14, 1969, 44/ 91,269 Int. Cl. B44f 1/10 US. Cl. 161-33 10 Claims ABSTRACT OF THE DISCLOSURE A heat-sensitive stencil sheet comprising:

(a) A thin porous support having a thermoplastic resin film bonded to one surface thereof with an adhesive containing a heat-sensitive component which undergoes a visible color change at a temperature of from about 80 C. to 180 C. together with at least one heat-fusible compound which is a metallic salt of a fatty acid containing from about 10 to 22 carbon atoms and forms a transparent melt at a temperature of from about 50 C. to

150 C.; or

(b) A thin porous support having a thermoplastic film bonded to one surface thereof with an adhesive, said film being coated with a mixture containing a heat-sensitive component which undergoes a visible color change at a temperature of from about 80 C. to 180 C. together with at least one heat-fusible compound which is a metallic salt of a fatty acid containing from about 10 to 22 carbon atoms and forms a transparent melt at a temperature of from about 50 C. to 150 C.

BACKGROUND OF INVENTION This invention relates to heat-sensitive stencil sheets prepared by affixing a film comprising a thermoplastic resin to the surface \of a porous thin support, usually paper. More particularly, it relates to a heat-sensitive stencil sheet for use in mimeographic printing which may be converted to stencils with readily visible colored images on their top surface.

Heat-sensitive stencil sheets are normally prepared to contain a thermoplastic resin film adhesively bound to a porous supporting sheet. Typical thermoplastic resins which may be employed include polystyrene, polyethylene, polypropylene, polyethylene and vinylidene chloridevinyl chloride copolymers. Copolymers of vinylidene chloride-vinyl chloride are especially favored. The thickness of the resin film is normally from about 5-10 microns. The weight of the porous supporting sheet is usually from about 8-18 g./m. It may be prepared, for example, from natural fibers obtained from mitsumata, paper mulberry, Manila hemp, and the like, or synthetic fibers such as rayon, polyvinyl alcohol synthetic fiber, polyethylene terephthalate synthetic fiber, acrylic resin, polyamide, or the like. Other thermoplastic resins may be used in the film and other materials may be used to form the porous support sheet.

The stencil sheets are used to prepare stencils and these in turn are utilized in the preparation of copies of an original. In the usual practice, the original having the desired image is superposed upon the thermoplastic film surface of the stencil sheet and the original is exposed to electromagnetic waves, including infrared rays, usually from the porous support side of the stencil sheet. The infrared rays are absorbed by the image and converted to heat energy. The heat produced effects perforations of the film in areas congruent to the image areas of the original. Because the support is porous the resulting 3,715,263 Patented Feb. 6, 1973 stencil may be used to transfer ink to a copy sheet to reproduce the original thereon.

The intensity of the electromagnetic waves, i.e. the amount of exposure of the stencil sheet to such waves, will, of course, influence the clarity of the perforated image on the stencil. If the exposure is insuflicient the perforated image will be defective and there will result an indistinct image when the stencil is used for printing. If the exposure is excessive a similar result will be observed. Since the thermoplastic resin film on the porous support of the stencil sheet is extremely thin it is difiicult to judge by observation with the naked eye whether the perforated image on the stencil is one which will be capable of producing clear printed images. In the past it has been necessary to make such a determination by a trial and error method in which a number of stencil sheets are prepared and actually utilized in printing. The prints obtained are then compared to determine which of the several stencils is most suitable for the production of new copies. This procedure is expensive and time-consuming.

THE INVENTION Heat-sensitive stencil sheets have now been discovered from which stencils, the suitability of which for printing can be readily determined by visual observation with the naked eye, can be prepared. The stencil sheets of this invention comprise a thin porous support having a thermoplastic resin film bonded to one surface thereof with an adhesive containing a heat-sensitive component which undergoes a visible color change at a temperature of from about C. to 180 C. together with at least one heatfusible compound which is a metallic salt of a fatty acid containing from about 10 to 22 carbon atoms and forms a transparent melt at a temperature of from about 50 C. to 150 C. Alternatively, the heat-sensitive component and the heat-fusible compound may be contained in a coating on the top surface of the thermoplastic resin film.

Adhesives which may be employed for the preparation of the heat-sensitive stencil sheets of this invention may be any of those adhesives which are conventionally used in the preparation of ordinary stencil sheets. Vinyl adhesives, particularly those prepared from polyvinyl acetate, vinyl acetate-ethylene copolymers, vinyl acetatemaleic acid copolymers, vinyl acetate-methylacrylate copolymers, vinyl acetate-acrylic acid copolymers, vinyl acetate-butyl methacrylic copolymers, and vinyl acetate crotonic acid copolymers are useful. Acrylic adhesives, particularly polyacrylic or polymethacrylic acid adhesives or their corresponding esters as well as acrylonitrile-methacrylic acid copolymers are especially favored. Commercial adhesives of this class include, for example, Gohsenyl M-SO Y-5, available from Nippon Synthetic Chemical Industry Co., Ltd., which is reported to be a methanol solution of a vinyl acetate homopolymer with a degree of polymerization of about 1100; Krehalon-SN which is reported to be a solution of a vinylidene chlorideacrylonitrile copolymer and is available from Kureha Chemical Industry Co. Ltd., and Super Dain FD- which is reported to be an alcoholic solution of an acrylic resin and is available from Nissetsu Industry Co. Ltd.

Typically the adhesive will be utilized in alcoholic solution and the heat-sensitive component together with the heat-fusible compound can be similarly dissolved or susended in the alcoholic solution. It is, of course, possible that the adhesive may be a suspension of fine particles in a liquid medium. In any event, the adhesive composition containing the heat-sensitive component and the heatfusible compound is coated onto the thin porous substrate and the liquid evaporated.

The heat-sensitive component and the heat-fusible compound will be selected so as to change color and fuse,

respectively at the temperature at which the thermoplastic film becomes perforated. This may be in the temperature range from about 80 C. to 180 C. but with most films will be from about 120 C. to 170 C. The component may be a single compound or complex which changes color when exposed to heat or it may be a mixture of reactants which react together under the influence of heat to produce a new compound and to thereby effect a concurrent color change. In any event, upon irradiation of the stencil sheet with infrared rays and resulting per foration of the thermoplastic film a transparent or opaque colored visible image reproducing the image of the original is formed.

The amount of heat-fusible compound in the adhesive for the preparation of the stencil sheets of this invention is desirably in the range of from about 0.1 to 1.0 part by weight for each part by weight of adhesive. The amount of visibly reactive heat-sensitive component is similarly from about 0.1 to 1.0 part by weight per part by weight of adhesive. In each instance the preferred range from the point of view of economy and ease of operation is from about 0.2 to 0.5 part by weight per each part of adhesive.

The weight of the adhesive layer including the heatsensitive component and the heat-fusible compound is typically in the range of from about 0.5 to 5.0 g./m. When the weight of the adhesive content is from about 0.5 to 5.0 g./rn. heat-sensitive stencil sheets from which one can easily determine the appropriate amount of exposure to infrared radiation for the purpose of producing stencils suitable for use in mimeographic, rotary press printing, and the like, which will accurately reproduce the original image, can be prepared. While appreciable variations from this range are possible there is a general tendency towards lack of clarity in the perforated image as more or less of the adhesive, heat-sensitive component or heat-fusible compound is employed. If a quantity of adhesive which is much less than 0.5 g./m. is employed the thermoplastic film may not be adequately bound to the porous substrate and if the amount of adhesive greatly exceeds 5 g./m. the perforation efficiency of the stencil sheet may be adversely affected.

If the stencil sheet is prepared to have a coating containing the heat sensitive component and heat fusible compound, a solution or dispersion of these ingredients in an appropriate solvent such as alcohol alone, a mixed solution of alcohol and ether or a mixed solution of alcohol and keto alcohol is coated on the top surface of the thermoplastic film of a stencil sheet prepared in advance by afiixing the film to a porous thin supporting sheet with an adhesive, thereby forming a coating of a heat sensitive visibly reactive component and a heat fusible compound. Alternatively the film may be initially coated with the active ingredients and the coated film subsequently bonded to a porous thin substrate with an adhesive.

Suitable solvents for use in coating the visibly reactive heat-sensitive component and heat fusible compound include alcohols such as ethanol, n-propanol, n-butanol and 2-ethyl butanol, ethers such as ethylene glycol-monomethyl ether, ethyleneglycol-monobutyl ether and diethyleneglycol-monoethyl ether, and keto alcohols such as diacetone alcohol. The visibly reactive heat-sensitive component and the heat fusible compound may be applied to the top surface of the film as a solution or a dispersion which may contain a small amount of the same adhesive which is used to bond the porous thin suporting sheet to the film. When the visibly reactive heat-sensitive component and the heat fusible compound are thus applied to the surface of film under the form of a solution or dispersion in an appropriate liquid which may contain an adhesive the surface of film is somewhat eroded by the liquid or the adhesive, thereby causing the component and the compound to be bonded more firmly to the surface of film.

The composition of a coating of this invention which contains a heat fusible compound and the visibly reactive heat-sensitive component is desirably mixed with the compound ranging from about 0.1 to 1 part by weight per one part by weight of said component. Typically the weight of heat-sensitive component and heat fusible compound coated on the surface of the film will be from about 0.1 gr./m. to 3.0 gr./rn. If the weight deviated appreciably from this range it becomes difficult to judge the proper amount of exposure and there is interference with the perforation effciency. For example if the weight is as high at 6.0 g./m. it is extremely difficult to form a satisfactory image.

Any of a wide variety of heat-sensitive components may be used in this invention including those already known for the production of heat-sensitive copy sheets. Typical examples of known components include those listed below.

(a) Complex compounds which change in color at a temperature range between from 50 C. to C. These complex compounds are described in Japanese patent publication No. 14,509/ 1966 (applicant: Kabushiki Kaisha Ricoh), and include such complex compounds as, for example,

hexamethylenetetramine-cobalt chloride (COC12'2C5H12N4'10H20) (yellow-red) hexamethylenetetrarnine-cobalt iodide (light yellow-red), hexamethylenetetramine-cobalt bromide (light yellowred), hexamethylenetetramine-nickel chloride (light green), hexamethylenetetramine-nickel bromide (light green), hexamethylenetetraminc-cobalt nitrate or coblat surfate and hexamethylenetetramine-nickel nitrate or nickel sulfate.

(b) Mixtures which comprise compounds having a secondary alcoholic hydroxyl radical and a melting point ranging from 100 C. to C. together with sulfur, a metal acetate or an inorganic metallic salt.

Such mixtures are described in Japanese patent publication No. 14,510/ 1966 (applicant: Kabushiki Kaisha Ricoh).

Typical examples of compounds having a secondary alcoholic hydroxyl radical include benzoin and its derivatives such as Z-methoxybenzoin, 4-chlorobenzoin, 4-dimethylaminobenzoin and Z-chloro 4 dimethylaminobenzoin; carbinols such as diphenylcarbinol, phenolic compounds such as resorcinol, pyrogallol, 3 hydroxytoluene 4 sulphonic acid, 4-nitroresorcinol and 4,6-dibromoresorcinol; aliphatic polyhydric alcohols such as erythritol, sorbitol, galactose, maltose, mannitol and saccharose.

Typical metallic salts include those which produce colored-sulfide compounds by reaction with sulfur such as sulfates, nitrates, carbonates and acetates of copper, lead, tin, molybdenum, cobalt, chromium, nickel, manganese, titanium, antimony, rhodium, mercury, iron, barium, bismuth, arsenic, magnesium, indium and iridium.

(c) Mixtures including compounds having a secondary alcoholic hydroxyl radical as described in (b) together with sulfur and a complex compound such as described in (a). These mixtures are described in Japanese patent publication No. 14,511/ 1966 (applicant: Kabushiki Kaisha Ricoh).

(d) A mixture of a carbohydrate and a dehydrating agent such as are described in Japanese patent publication No. 13,237/ 1967 (applicant: Kabushiki Kaisha Ricoh). Typical mixtures described in this publication include, for example, saccharose, fructose, galactose and starch as the carbohydrate, and sulfuric acid, acetic anhydride, zinc chloride anhydride and 'P-toluenesulfonic acid as the dehydrating agent.

(e) Mixtures which comprise an iron salt of fatty acid having a long chain such as ferric stearate and ferric myristate and phenol or a phenolic compound such as tannic acid, gallic acid and ammonium salicylate.

(f) Mixtures containing a heavy metal salt of an organic acid such as nickel, cobalt, lead, copper, iron, mercury or silver salts of acetic, stearic or palmitic acid and an alkaline earth metal sulfide such as calcium, strontium or barium sulfides. These same heavy metal salts of organic acids may be used in association with an organic chelate compound such as s-diphenylcarbazide or diphenylcarbazone.

(g) Mixtures comprising a heavy metal oxalate such as silver, lead, mercury or thorium oxalate and a sulfurcontaining compound such as sodium-tetrathionate, sodium thiosulfate and thiourea.

(h) Mixtures including a ferric salt of a fatty acid such as ferric stearate and an aromatic polyhydroxy compound such as 3,4-dihydroxytetraphenylmethane.

(i) Mixtures of a noble metal salt of organic acid such as silver or mercury oxalate and an organic polyhydroxy compound including such polyhydroxy alcohols as glycerin and glycol.

(j) Mixtures of a noble metal salt of an organic acid such as silver behenate or silver stearate and an aromatic reducing agent such as protocatechuic acid, spiroindane or hydroquinone.

(k) Mixtures of an iron salt of a fatty acid such as ferric pelargonate or ferric laurate and a derivative of thiosemicarbazide or isothiosemicarbazide.

(l) Mixtures of a lead salt of an organic acid such as lead capronate, lead pelargonate or lead behenate and a thiourea derivative such as ethylene thiourea and N- dodecyl thiourea.

(In) Mixtures including a heavy metal salt of a higher fatty acid such as ferric stearate or copper stearate and zinc-dialkyldithiocarbamate.

(n) A mixture which forms an oxazine dye such as a combination of resorcinol and a nitroso compound, or a mixture which forms an azo dye.

Heat-fusible compounds useful in this invention include metallic salts of saturated or unsaturated higher fatty acids having from about to 22 carbon atoms such as stearic acid, palmitic acid, lauric acid, myristic acid, oleic acid, erucic acid, behenic acid, etc., and at least one of these metallc salts is employed for mixing in the resinous solution for forming said ink-impermeable film. A wide variety of metals are applicable including metals belonging to Group II of the Periodic Table such as calcium, zinc, cadmium, magnesium, etc.; lead belonging to Group IV; manganese belonging to Group VII; iron, cobalt, nickel, etc. belonging to Group VIII and; in addition, those salts combined with such metals as copper belonging to Group I are suitable.

While fatty acids having less than 10 or more than 22 carbon atoms may be employed they are generally not practical. Those acids on the lower end of the range have offensive odors, and those on the higher end are difficult to obtain and are expensive. These heat-fusible compounds have the melting points from about 70 C. to 150 C. They should, of course, be reaction inert with respect to the heat-sensitive component.

A particular advantage of this invention is that visibly reactive heat sensitive components which develop such a low density image that they are not useful in the preparation of heat sensitive copy sheets may be employed to produce stencil sheets. A copy sheet is a sheet which upon exposure to heat generated by absorption of infrared rays on an image to be copied will reproduce the image by the reaction of heat sensitive components contained therein.

The adhesive, Whether or not it contains the active ingredients may be coated onto the thin porous substrate or onto the film in any convenient manner, for example by roller coating, spraying or the like. A coating on the thermoplastic film may be similarly laid down.

Stencils are prepared from the stencil sheets of this invention in the usual manner and, as expected, perforation takes place in the area of the ink-impermeable film congruent with the image area of the original. However, the

visibly reactive heat-sensitive component develops colors in the perforated areas and the melt concentrates at the edge of the perforated area to present a sharply outlined colored image. The presence of the heat-fusible compound causes the perforated image to be even more sharply outlined with improved clarity of color. Moreover, since the extra-fine particles of the colored melt adhere to the fibers of the porous thin paper, the perforated area can be readily observed by the naked eye. The perforated area constitutes no obstacle to the permeability of the printing ink. It is readily possible to determine the optimum amount of infrared radiation and to foresee, from the clarity of the visible image on the stencil, the quality of the prints which can be produced.

The following non-limiting examples are given by way of illustration only:

Example 1 To 1500 ml. of a 4.5%-methanol solution of vinyl acetate homopolymer were added 10 gr. of zinc stearate and 10 gr. of calcium stearate. The resultant mixture was mixed well for 3 hours in a. ball mil, and 2.0 gr. of diphenylcarbazone were added to prepare an adhesive solution containing the heat fusible compound and the visibly reactive heat-sensitive component.

Subsequently, a 7,:r-thick transparent film comprising vinylidene chloride-vinylchloride copolymer as its principal component and a 30/L-thl0k porous thin supporting paper comprising manila hemp fibers as its principal component and weighing 9 gr. per square meter were affixed together by employing the foregoing adhesive solution.

The application of the adhesive was effected by roll coating, and the amount of adhesive on the porous thin supporting paper was about 2.2 g./rn. A newspaper was superposed on the surface of the film of thus prepared stencil sheet, and the infrared-ray irradiation was applied (by employing Thermofax manufactured by 3-M Co., Ltd.) from the paper side of the stencil sheet to effect perforation. The image formed was a clearly visible red against a pink background. The stencil was employed for printing with a commercial mimeograph machine, and proved capable of producing a multiplicity of clear-cut prints which faithfully reproduced the original image.

Determination of the optimum amount of infrared-ray irradiation for the production of the most useful stencils could easily be achieved by visual observation. If the stencil did not appear to be satisfactory the irradiation could be repeated. It was found that the optimum amount of irridation for processing an original of A4 size superposed on the stencil sheet of this example was about 4 seconds.

For the purpose of comparison, 4 stencils were identically prepared except that the adhesive did not contain the color affecting ingredients. They were developed in the usual way utilizing Thermofax for about 3 seconds, 4 seconds, 5 seconds and 6 seconds respectively. The perforated images formed on each stencil were almost illegible and it was impossible to judge which was properly exposed. When the stencils were employed for printing with a commercial mimeographic machine, the prints obtained utilizing the stencil prepared by exposing to irradiation for about 4 seconds was capable of accurately reproducing the original image, but all the remaining stencils produced only indistinct prints.

Example 2 sequently, by applying the thus prepared adhesive solution to a film and a porous thin supporting paper, the same as that employed in Example 1, a stencil sheet comprising the supporting paper and with the film bonded onto one surface with the adhesive was obtained.

When the thus prepared stencil sheet was subjected to infrared-ray irradiation in the same manner as in Examby weight of at least one heat fusible compound which is a metallic salt of a fatty acid containing from about 10 to 22 carbon atoms and forms a transparent melt at a temperature from about 50 C. to 150 C.

ple 1, a stencil carrying a clearcut, dark brown and 2. A stencil sheet as in claim 1 wherein the heat-sensilegible perforated image, clear against a white backtive component is a single component which undergoes a ground, and suitable for use in mimeographic printing color change at a temperature of from about 80 C. to was obtained. The optimum amount of exposure was 180 C. readily defefmined y Visual 0b$ ?rV at1011 aS in P 3. A stencil sheet as in claim 1 wherein the heat-sensil Stencll f pl y for Prlntlng Wlth a commefclal 10 tive component is a mixture of at least two reactants P It 1 to Capabla 9 P which react at a temperature of from about 80 C. to f f a 11111101111010 0f Pfmts faithfully P QduClng the 180 C. to form a new compound and effect a concurrent original. color change.

Example 3 4. A stencil sheet as in claim 1 wherein the thermo- By employing various visibly reactive heat-sensitive plastic film is a copolymer of vinylidene chloride and components and heat fusible compounds and a 4.5 vinyl chloride and is from about 5 to 101.0 thick. methanol solution of polyvinylacetate, heat-sensitive sten- 5. A stencil sheet as in claim 1 wherein the support cil sheets were prepared in accordance with the methods is paper and weighs from about 8 to 18 g./m. described in Examples 1 and 2. The perforation efiiciency 6. A heat-sensitive stencil sheet comprising a thin of the stencil sheets thus obtained, when subjected to 20 porous support having a thermoplastic film perforable infrared-ray exposure in accordance with the procedure of by heat at a temperature from about 80 C. to 180 C. Example 1 was equal to that observed with the stencil bonded to one surface thereof with an adhesive, said sheets of Examples land 2. film being coated with from about 0.1 g./m. to 3.0

The following table shows some of the combinations g./m. of a mixture containing, for each part by weight employed: of coating, from about 0.1 to 1.0 parts by weight of a Mixing ratio: (Q/( Stencil (a) Vls1bly reactive (b) Heat fusible (part by sheet No. heat'sensitive component compound weight) Color 1 Hexamethylene tetrarnine'cobalt chloride Lead palmitate 3/1 Blue. 2 Fern'c steratate and gallic acid (3:1) Manganese stearate. 2/1 Blackish brown. 3 Lead oxalate and thiourea (1:1) Potassium palmitate 3/1 Do. 4 Silver behenate and protocatechuic a (6:1). Zine stearate 2. 3/1 Do. 5- Ferric laurate and thiosemicarbazide Magnesium myristate 2. 8/1 Do. 6 Cupic stearate and zinc dialkyldithiocarbamate Cobalt myn'state 2. 5/1 Do.

Example 4 heat sensitive component which undergoes a visible color To 800 ml. of 4.5 %-methanol solution of polyvinyl ace- 40 change to form a colored lmage g the porolls support at a temperature of from about 80 C. to 180 C. together tate there was added 10 gr. of nickel laurate as a heat with for each art b Wei ht of coafn from b t 01 fusible compound and a visible reactive heat-sensitive to art b g of i least i f 3 2 component consisting of 20 gr. of diphenyl nitrosamine p g u pound WhlCh 1s a metallic salt of a fatty acid contaimng and 5 gr. of protocatechuic acid. The sol1d was dispersed f b t 10 22 b d f in the S 01 mi on. rom a 0111 to car on atirm an borms a trans- The resultant dispersion was applied onto a 7 -thick, iggi at a temperature 0 mm out to transParent film contqmmg. vinyhdene chlonde'vmyl' 7. A heat-sensitive stencil sheet as in claim 6 wherein chlorlde copolymer at its principal component and was the heat-sensitive component is a single component which dned thereby formmg a coating of the aforesmd com under oes a color chan e at a tem erature of from about ponent and the compound on the surface of said film. 50 to 180 C g P Subsequently by employmg an adheslv-e slmllar m that 8. A heat-sensitive stencil sheet as in claim 6 wherein of Example 1 the film was bonded to a thin paper support th h e eat-sensitive component 1s a mixture of at least two leaving the coating exposed to prepare a stencil sheet. reactants which react at a tem perature of from about When thus prepared stencil sheet was developed in the C to C t f n6 d and if t same manner as in Example 1, there was obtained a stencil III t l mm a W compoun 6 6c a with a clear-cut, blackish brown and legible perforated g G0 f, ange' tin The eat-sensitlve stencil sheet as 1n cla1m 6 wherein image suitable for use 1n mimeograp 1c prm g th h 1 film 1 f d hl dil determined e t ermop astic 1s a copo ymer o viny 1 ene c oadequacy of the perforated lmage was rea y as em 10 ed for nde and vmyl chloride and 1s from about 5 to 10,11. thick. by v1sual observatlon. When the stencl w p y 10 A h h hi0 machine it eat-sens1t1ve stencil s eet as 1n claim 6 wherein prmtmg Wlth commerclal mlme-og-rzip 3 the su ort is a er and weighs from about 8 to 18 /m 3 proved capable of producing a multlphcity of prints faith- PP P P gf y reproducing the orlgmal- References Cited What is claimed is:

'1. A heat-sensitive stencil sheet comprising a thin UNITED STATES PATENTS porous support having a thermoplastic resin film pcr- 1,753,204 4/1930 Horii .117 35,5 forable by heat at a temperature of from about 80 C. 2,354,855 8/ 1944 Emanuel 215 40 to 180 C. bonded to one surface thereof with from 2,663,654 12/ 1953 Miller et al 11736.8 about 0.5 to 5 g./m. of an adhesive containing, for each 2,663,657 12/ 1953 Miller et al 117 36 8 part by weight of adhesive compound, from about 0.1 2,693,426 11/1954 Hoover et al 117 35 5 to 1.0 parts by weight of an (a) heat sensitive component which undergoes a visible color change to form a colored MORRIS SUSSMAN, Primary Examiner image on the porous support at a temperature of from S Cl XR about C. to C. together with, for each part by weight of adhesive compound from about 0.1 to 1.0 parts 75 161- 159, 410, 251; 117-355 

